Universal unit strip/carrier frame assembly and methods

ABSTRACT

A method of making a microelectronic assembly includes providing a flexible tape having first and second surfaces with a plurality of connection components in a central region of the flexible tape, providing a carrier frame having top and bottom surfaces and a slot extending therebetween and placing the flexible tape in contact with the top surface of the carrier frame. Next a resilient element is provided on each connection component and the flexible tape is passed through the slot so that the flexible tape disengages from the top surface of the carrier frame, passes through the slot and engages the bottom surface of the carrier frame. The carrier frame includes one or more interior edges defining the slot and a cut-out region contiguous with one end of the slot. The cut-out region also extends between the top and bottom surfaces of the carrier frame and the width of the cut-out region is greater than the width of the flexible tape so that at least one side border region of the flexible tape is pivotally secured to the carrier frame.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application SerialNo. 60/040,020 filed Mar. 4, 1997, the disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to microelectronic assembliesand more particularly relates to methods of mass producing semiconductorchip assemblies.

BACKGROUND OF THE INVENTION

A semiconductor chip is generally connected to an external circuitelement through contacts on the front face of the chip. For example inthe tape automated bonding process (hereinafter referred to as the "TAB"process), a dielectric sheet, such as a thin foil of polyimide, isprovided with one or more bond windows and an array of metallic leads onone surface thereof. Each lead has one end integrally connected toterminals on the dielectric sheet and an opposite end extendingoutwardly from a central portion of the dielectric sheet so that theoutermost ends of the leads project beyond the bond windows. Thedielectric sheet is juxtaposed with the semiconductor chip so that thebond windows are aligned with the contacts on the chip and so that theoutermost ends of the leads overlie the front face of the chip. Theleads are then bonded to the contacts of the chip using bondingtechniques such as ultrasonic or thermocompression bonding. After thebonding step, the terminals are connected to an external circuitelement, such as a printed circuit board, which electricallyinterconnects the chip and the printed circuit board.

Commonly assigned U.S. Pat. No. 5,148,266, the disclosure of which isincorporated by reference herein, discloses a method of manufacturingsemiconductor chip assemblies which are fabricated in a substantiallycontinuous sheet or strip. A plurality of connection components arespaced lengthwise along a continuous tape, each connection componenthaving terminals and flexible leads thereon. In one assembly method,semiconductor chips are connected to respective connection components onthe tape and the assembled semiconductor chips are then carrieddownstream with the tape for further processing steps.

Commonly assigned U.S. Pat. No. 5,659,952, the disclosure of which isincorporated by reference herein, provides methods of fabricating asemiconductor chip assembly having a compliant interface. In preferredmethods according to the U.S. Pat. No. 5,659,952 patent, a flexible,substantially inextensible dielectric film having a surface is providedand a plurality of compliant pads are attached to the first surface ofthe dielectric film, whereby any two adjacent compliant pads define achannel therebetween. Attaching the compliant pads to the dielectricfilm may be accomplished in a number of different ways. In oneembodiment, a stencil mask having a plurality of holes extendingtherethrough is placed on top of the first surface of the dielectricfilm. The holes in the stencil mask are then filled with a curableliquid elastomer. Desirably, liquid elastomer has a thick enoughconsistency so that the mask may be removed before curing the elastomer.After the mask has been removed, the elastomer is at least partiallycured using energy, such as heat or ultraviolet light. The holes in themask are preferably filled with the liquid elastomer by screening theliquid elastomer across an exposed surface of the mask such that theelastomer is deposited into the holes of the mask. Thus, there isprovided an assembly which includes an array or plurality of compliantpads defining channels therebetween, i.e. the channels run betweenadjacent compliant pads.

In further stages of the process disclosed in the U.S. Pat. No.5,659,952 patent, the assembly including the array of compliant pads isassembled to a second support structure, such as a semiconductor chiphaving a front face with contacts. During the assembly step, the frontcontact bearing face of the chip is abutted against the array ofcompliant pads and the contacts are electrically connected to terminalson a second surface of the dielectric film remote from the chip. Acompliant filler, such as a curable liquid elastomer, may then beinjected into the channels between the semiconductor chip and thedielectric film and around the compliant pads while the chip and thedielectric film are held in place. The curable liquid elastomer may thenbe cured to form a substantially uniform, planar, compliant layerbetween the chip and the dielectric film.

However, further improvements in handling of the components duringassembly processes, such as those described in the U.S. Pat. No.5,659,952 patent, would be desirable.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method ofmaking a microelectronic assembly includes the steps of providing aflexible tape having first and second surfaces and including a pluralityor array of connection components in a central region thereof. Theflexible tape typically includes a dielectric film, such as a polyimide,whereby each connection component includes a part of the dielectric filmhaving electrically conductive parts. The flexible tape includes one ormore border regions which surround the central region bearing theplurality of connection components. The electrically conductive partstypically comprise an array or plurality of conductive terminalsaccessible at one surface of the dielectric film and may also includeflexible leads integrally connected to the terminals. Each connectioncomponent also includes an attachment region for receiving a resilientelement, such as an array or plurality of compliant pads, as will bediscussed in more detail below. The attachment region of each connectioncomponent are preferably provided at the first surface of the flexibletape with the terminals preferably accessible at the second surface ofthe flexible tape.

A carrier frame, having a top surface and a bottom surface, is typicallyprovided for processing the flexible tape. The carrier frame isdesirably between approximately 250-400 microns thick and comprises arigid material, such as a metal or plastic. The carrier frame has one ormore inner edges which define a slot extending between the top andbottom surfaces thereof. In certain preferred embodiments the slot iselongated and the carrier frame includes a cut-out region which iscontiguous with one end of the slot, whereby the width of the cut-outregion is greater than the width of the slot.

In further stages of preferred assembly methods, the flexible tape isplaced on a top surface of a work holder and the carrier frame is placedover the flexible tape so that the second surface of the flexible tape(i.e., the terminal side) is in contact with the surface of the carrierframe. The width of the flexible tape is greater than the width of theslot. Therefore, when the flexible tape overlies the carrier frame andis substantially parallel to and in contact therewith, the side borderregions of the tape preferably extend beyond the one or more of theinner edges of the carrier frame. However, the width of the cut-outregion is greater than the width of the flexible tape so that portionsof the flexible tape overlying the cut-out region are typically boundedby the cut-out region.

In further stages of the process, one end of the flexible tape issecured to the carrier frame and is preferably hingedly or pivotallysecured thereto. In certain preferred embodiments, the portion of theflexible tape extending into the cut-out region is pivotally secured tothe carrier frame by affixing flexible strips to the border regions ofthe flexible tape overlying the cut-out region. The flexible strips maybe removed and desirably include an adhesive thereon which secures tothe border region of the tape. In certain preferred embodiments, eachflexible adhesive strip has a first end connected to the border regionsof the flexible tape overlying or extending into the cut-out region anda second end connected to the carrier frame.

In the next stage of the process, during a first processing operation, aresilient element is provided over the attachment region of eachconnection component. The resilient element may be provided by forming aplurality or array of compliant pads on each attachment region, such asby using the methods described in the aforementioned U.S. Pat. No.5,659,952 patent. The compliant pads are preferably formed by stencilingor screen printing an array of individual pads on each attachmentregion, whereby the array includes channels running between adjacentpads. During the step of providing the resilient elements on theattachment regions of the connection components, the flexible tape ismaintained in a substantially stationary position over the top surfaceof the carrier frame by supporting the underside of the flexible tape.This underside support may be provided using a supporting element, suchas a support plate, which passes through the slot in the carrier frameand engages the second surface of the flexible tape to prevent theflexible tape from flexing or moving downward during the providing aresilient element step. Although the present invention is not limited byany particular theory of operation, it is believed that the formation ofproperly aligned and shaped resilient elements is greatly facilitatedwhen the bottom of the stencil is in direct contact with the firstsurface of the flexible tape. This direct contact is not possible whenthe carrier frame lies between the bottom of the stencil and theflexible tape. For example, if the flexible tape was under the carrierframe, rather than overlying the top of the carrier frame, then it wouldbe impractical to place the bottom of the stencil directly in contactwith the first surface of the flexible tape because the stencil would bespaced from the first surface of the tape by the carrier frame. Asmentioned previously, this could result in the formation of misalignedand improperly shaped compliant pads on the various attachment regionsof the connection components. The compliant pads may then be at leastpartially cured, such as by using heat or ultraviolet light. In otherembodiments, the compliant pads may not be cured until after die attach,as will be discussed in more detail below.

After the compliant pads are formed on the attachment regions of theflexible tape, the tape is preferably passed through the slot in thecarrier frame by disengaging the borders of the tape from the topsurface of the carrier frame, passing the tape through the slot andreengaging the borders of the tape with the bottom surface of thecarrier frame. In accordance with one preferred embodiment of thepresent invention, the flexible tape initially overlies the top surfaceof the carrier frame with the second surface of the tape in contact withthe carrier frame and with one end of the tape pivotally connected tothe carrier frame. Preferably, the portion of the flexible tape which ispivotally connected to the carrier frame is that portion which overliesthe cut-out region of the slot. As the flexible tape is held in asubstantially stationary position, one end of the carrier frame isrotated about the pivotally secured portion of the flexible tape. Thecarrier frame is rotated upward between approximately 15-60° andpreferably between approximately 25-35° from the initial or firstposition toward a second position. As the carrier frame moves toward thesecond position, the second surface of the flexible tape disengages fromthe top surface of the carrier frame and passes through the slot. Afterthe flexible has disengaged from the top surface and passed through theslot, the carrier frame is then rotated downward approximately 25-35°from the second position back toward the first position, and preferablyall the way back to the first position, so that the bottom surface ofthe carrier frame engages or is in contact with the first surface of theflexible tape. During the passing the flexible tape step, the flexiblenature of the tape permits the border regions of the flexible tape tomove or flex toward one another so that the tape may pass freely throughthe slot. If the side borders of the tape were not capable of flexinginwardly, then the tape could not readily pass through the slot because,as mentioned above, the width of the flexible tape is greater than thewidth of the slot. After the passing step, the first surface of theflexible tape is in contact with the bottom surface of the carrier frameand the slot in the carrier frame overlies and is in substantialalignment with the central region of the flexible tape so that the slotoverlies the connection components, which in turn are accessible throughthe slot. In this stage of the assembly process, the resilient elementson the respective connection components face upwardly in the slot.

In the next stage of the assembly process, during a second processingoperation, microelectronic elements, such as semiconductor chips havingcontacts on a front face thereof, are assembled with the resilientelements of each connection component to provide microelectronicassemblies. The chips are preferably assembled to the resilient elementsby abutting the chips against the resilient elements. During theassembling step, the flexible tape is maintained in a substantiallystationary position, such as by using a supporting plate, to prevent thetape from flexing or moving. Supporting the underside of the flexibletape at this stage is important because if the tape flexed downwardduring assembly of the microelectronic elements, then the elements couldpossibly be misaligned over the connection components, thereby resultingin the production of defective chip assemblies.

After the die attach or assembly step, the microelectronic elements andthe connection components are electrically interconnected, such as bybonding the flexible leads of the connection components to the contactson the microelectronic elements, or by other known connecting processes.A curable liquid encapsulant, such as silicone elastomer, may then beprovided between the microelectronic elements and the connectioncomponents. The curable liquid encapsulant preferably flows between themicroelectronic element and the connection component, through thechannels between the compliant pads and around the flexible leads. Incertain embodiments, one or more coverlays may be used to prevent theliquid encapsulant from flowing into contact with the second surface ofthe connection components and/or surfaces of the chips, such as the backsurfaces of the chips. The curable liquid encapsulant may then be curedusing heat or ultraviolet light to provide a compliant interface foreach microelectronic assembly. The cured encapsulant also protects thefinal assembly, including the flexible leads, from contamination. Theassemblies may then be severed from the flexible tape by cutting aroundthe perimeter of the assembly to provide individual microelectronicassemblies, or groups of two or more assemblies, capable of beinginterconnected with external circuit elements such as printed circuitboards.

In further preferred embodiments, the slot in the carrier frame is anelongated slot having first and second ends and first and second sides,and the cut-out region at one end of the slot is contiguous with eitherthe first or second end of the slot. The flexible tape preferablyincludes an elongated strip having an array of connection components,such as an array of connection components aligned in a 3×10 matrix. Thesides of the flexible tape are preferably bound by border regions onopposite sides thereof so that when the flexible tape overlies thecarrier frame, and is substantially parallel thereto, the side borderregions of the flexible tape extend beyond the sides of the elongatedslot. However, the side border regions of the flexible tape extendinginto the cut-out region do not extend beyond the sides of the cut-outregion because the width of the cut-out region is greater than the widthof the flexible tape. Thus, during the pivotally securing stepsdescribed above, when the flexible strips are applied, to pivotallysecure the tape to the carrier frame, the one or more strips arepreferably attached to the portions of the side border regions extendinginto the cut-out region. Without the oversized cut-out region, it wouldbe difficult to pass or transfer the flexible tape from one surface ofthe carrier frame to the opposite surface of the carrier frame while theflexible tape remained secured to the carrier frame.

Thus, by using a carrier frame having an elongated slot and a cut-outregion as described above, it is possible to easily handle andmanipulate the connection components and microelectronic assembliesthrough all of the assembly steps to the final severing operation. Theflexible tape can be easily moved between the top and bottom surfaces ofthe carrier frame to provide unfettered access to the first and secondsurfaces of the flexible tape as required during different stages of theassembly process. The ability to quickly and easily transfer the tapefrom the top of the carrier frame to the bottom of the carrier framesimplifies the assembly process and minimizes handling of the flexibletape and the microelectronic elements. Moreover, the carrier frames canbe readily manipulated (i.e. inverted) during the various assembly stepsand are inexpensive to manufacture.

In another embodiment of the present invention, the carrier frame issubstantially similar to that described above; however, the elongatedslot includes teeth or projections which extend from opposite sides ofthe slot and toward the center of the slot. The side borders of theflexible tape contact the teeth to maintain the tape on the top orbottom surface of the carrier frame, as may be required during variousstages of the assembly process. The flexible tape is pivotally connectedto the carrier frame so that the tape can pivot between engagement withthe top and bottom surfaces of the carrier frame as described above.

In another embodiment, an apparatus for processing flexible tapepivotally secured to a carrier frame which has a top surface and abottom surface and a slot extending therebetween includes a base havinga top surface and a bottom surface and including an aperture extendingtherebetween and a platform having a top surface and being sized to fitwithin the aperture in the base. The base is pivotally secured to oneend of the platform and is movable between a first position wherein thetop surface of the base is substantially parallel to the top surface ofthe platform and a second position wherein the top surface of the basehas been pivoted between approximately 15-60°, and preferably between25-35° above the top surface of the platform. The carrier frame includesalignment apertures and the top surface of the base includes alignmentposts so that the carrier frame may be aligned over the top surface ofthe base, whereby the slot in the carrier frame is aligned over theaperture in the base and the platform. The apparatus also includes aclamp which has a perimeter which is sized to pass through the slot inthe carrier frame and the aperture in the platform so that the clamp maysecure the flexible tape to the top surface of the platform as theplatform moves between the first and second positions. The platformincludes a securing element at the top surface thereof, such as aplurality of vacuum holes. The clamp and the vacuum holes cooperativelysecure the flexible tape to the top surface of the platform as the basepivots between the first and second positions. The top surface of theplatform is approximately 500-700 microns higher than the top surface ofthe base when the base is in the first position.

The foregoing and other objects and advantages of the present inventionwill be better understood from the following detailed description ofpreferred embodiments taken together with the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a top view of a first surface of a flexible tape includinga plurality of connection components according to one embodiment of thepresent invention.

FIG. 1B shows a bottom view of FIG. 1A depicting a second surface of theflexible tape.

FIG. 1C shows a fragmentary side view of FIG. 1A.

FIG. 2A shows a top view of a work holder for supporting the flexibletape shown in FIGS. 1A-1C.

FIG. 2B shows a side view of FIG. 2A.

FIG. 3A shows a top view of the flexible tape shown in FIGS. 1A-1C onthe work holder shown in FIGS. 2A-2B.

FIG. 3B shows a side view of FIG. 3A.

FIG. 4A shows a top view of a carrier frame used in one embodiment of amethod of making microelectronic assemblies according to the presentinvention.

FIG. 4B shows a side view of FIG. 4A.

FIG. 5A shows a top view of the carrier frame shown in FIGS. 4A-4Boverlying the flexible tape shown in FIGS. 1A-1C and the work holdershown in FIGS. 2A-2B.

FIG. 5B shows a side view of FIG. 5A.

FIG. 6 shows a top view of FIG. 5A after the flexible tape has beenpivotally connected to the carrier frame.

FIG. 7 shows a detailed fragmentary view of the end of the flexible tapepivotally connected to the carrier frame.

FIG. 8A shows a top view of the pivotally connected flexible tape shownin FIGS. 6 and 7 after the carrier frame has been inverted.

FIG. 8B shows a side view of FIG. 8A.

FIG. 9A shows a front view of a storage magazine used for storing thepivotally connected flexible tape shown in FIGS. 8A and 8B

FIG. 9B shows a detailed fragmentary view of the storage magazine shownin FIG. 9A.

FIG. 10A shows the orientation of the flexible tape and the carrierframe shown in FIG. 8B after the carrier frame has been removed from thestorage magazine.

FIG. 10B shows a fragmentary side view of the flexible tape whilecompliant pads are being formed on the first surface thereof.

FIG. 10C shows a top fragmentary view of the flexible tape shown in FIG.10B after the compliant pads have been formed thereon.

FIG. 11 shows a perspective view of a pivoting apparatus for processingthe flexible tape shown in FIGS. 1A-1C.

FIGS. 12A and 12B show respective top and side views of a work holderfor the pivoting apparatus shown in FIG. 11.

FIGS. 13A and 13B show respective side and end views of a clamp for thepivoting apparatus shown in FIG. 11.

FIG. 13C shows the clamp shown in FIG. 13B in contact with the topsurface of the flexible tape shown in FIGS. 1A-1C.

FIG. 14A shows a top view of the flexible tape and carrier frame of FIG.10A overlying the work holder shown in FIG. 12A.

FIG. 14B shows a side view of FIG. 14A.

FIG. 15A shows a top view of FIG. 14A including the clamp shown in FIGS.13A and 13B.

FIG. 15B shows a side view of FIG. 15A.

FIGS. 16A and 16B show the pivoting assembly of FIG. 15B during furtherstages of a method for passing the flexible tape through a slot in thecarrier fame.

FIG. 17A shows a top view of the flexible tape after is has been passedthrough the slot in the carrier frame.

FIG. 17B shows a fragmentary side view of FIG. 17A.

FIG. 18 shows the flexible tape of FIG. 17A after the carrier frame hasbeen inverted.

FIG. 19 shows the flexible tap shown in FIG. 18 during further stages ofan assembly method according to the present invention.

FIG. 20 shows a fragmentary side view of FIG. 19 during further stagesof an assembly method according to the present invention.

FIG. 21 shows another embodiment of the carrier frame shown in FIG. 4A.

FIG. 22 shows an inverted view of FIG. 20, during still further stagesof an assembly method according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1A-1C, in one embodiment of the present invention aflexible tape 20 includes a flexible sheet-like dielectric film, such asa polymeric material, and has a first surface 22 and a second surface24. The flexible tape includes a plurality of connection components 26which are arranged in a 3×10 array. The flexible tape strip 20 isprovided by severing a section of the tape from a continuous reel. Eachconnection component 26 includes a part of the flexible dielectric filmhaving an attachment surface 27 at the first surface 22 of the flexibletape and a plurality or array of terminals 28 at the second surface ofthe flexible tape. Each connection component 26 also includes flexibleleads 30 integrally connected to the terminals 28. Each connectioncomponent 26 serves as a compliant interface for a microelectronicelement (not shown), such as a semiconductor chip, so that themicroelectronic element may be electrically connected to an externalcircuit element via the connection component 26. The connectioncomponent 26 is preferably formed from a polymeric material such asKAPTON(E) available from DuPont Chemical Corporation having anapproximate thickness between 25 to 75 microns. The connection component26 includes bond windows 29 for accessing the flexible leads 30 in orderto bond the flexible leads 30 to contacts on the microelectronic elementduring a bonding operation, as will be discussed in more detail below.The array of connection components 26 are disposed within a centralregion of the flexible tape 20. The tape 20 has a first end 32 and asecond end 34 and side portions which are bounded by a first border 36and a second border 38. The side borders 36 and 38 include sprocketholes 40 formed therein for handling and moving the flexible tape 20during fabrication of the tape and during the various assembly steps.

FIGS. 2A and 2B show a work holder 42 for supporting the flexible tape20 during certain stages of the assembly process. The work holder 42includes an array of vacuum holes 44 formed at the top surface 46 of thework holder 42. When the flexible tape 20 is placed on the top surface46 of the work holder 42, the vacuum holes 44 are preferably insubstantial alignment with the central region of the flexible tape 20.The work holder 42 also includes a first set of tape alignment posts 48and a second set of tape alignment posts 49 for aligning the flexibletape 20. During an alignment operation, two or more of the sprocketholes 40 are aligned with the tape alignment posts 48 and 49 as theflexible tape 20 is lowered onto the top surface 46 of the work holder42. The flexible tape 20 may be removed from the top surface of the workholder 42 and realigned if visual observation indicates that theflexible tape 20 has not been properly aligned on the work holder 42.The work holder 42 also includes a set of carrier frame alignment posts50 projecting from the top surface thereof. The carrier frame alignmentposts 50 are used to align the carrier frame over the work holder, aswill be described in more detail below.

FIGS. 3A and 3B show the flexible tape 20 after the tape has beenaligned with the tape alignment posts 48 and 49 positioned on the workholder 42. The flexible tape 20 is positioned on the work holder 42 sothat the first surface 22 of the flexible tape 20 is in contact with thetop surface 46 of the work holder 42 and the second surface 24 of thetape 20 faces away from the top surface 46 of the work holder 42.

Referring to FIGS. 4A and 4B, in the next stage of the assembly process,a carrier frame 52 having a top surface 54 and a bottom surface 56 andincluding an elongated slot 58 formed in the center thereof is provided.The slot 58 has a first end 60 and a second end 62 and first and secondopposed sides 64 and 66 which are defined by one or more interior edges70 of the carrier frame 52. The carrier frame 52 also includes a cutoutregion or portion 72 integral with the second end 62 of the slot 58. Thewidth of the cut-out portion 72 is greater than the width of the slot 58for reasons which will be explained in more detail below. The carrierframe includes tape alignment apertures 74 and 75 for receiving therespective flexible tape alignment posts 48 and 49 of tape the workholder when the carrier frame 52 is placed over the work holder 42 and asecond set of apertures 76 for receiving the carrier frame alignmentposts 50.

FIGS. 5A and 5B show further stages after the carrier frame 52 has beenprovided over the second surface of the flexible tape 20 and the workholder 42. During this step, the top surface 54 of the carrier frame 52is juxtaposed with the top surface 46 of the work holder 42. The slot 58in the carrier frame 52 overlies the central region of the flexible tape20 including the plurality of connection components 26. Before thecarrier frame 52 is positioned over the work holder 42, the flexibletape alignment posts 48 and 49 are aligned with the respective tapealignment apertures 74 and 75 in the carrier frame 52 and the carrierframe alignment posts 50 are aligned with the carrier frame alignmentapertures 76 in the carrier frame 52. The carrier frame 52 is thenlowered into engagement with the top surface 46 of the work holder 42 sothat the top surface 54 of the carrier frame 52 is in contact with thesecond surface 24 of the flexible tape 20. The width of the flexibletape 20 is greater than the width of the slot 58 so that the sideborders 36 and 38 extend beyond the sides 64 and 66 of the slot 58.However, the second end 34 of the flexible tape 20 which extends intothe cut-out region 72 is bounded by the cut-out region so that theborders are visible and can be accessed from the bottom of the carrierframe 52.

Referring to FIGS. 6 and 7, the second end 34 of the flexible tape 20 isthen pivotally connected to the carrier frame 52 by placing flexiblestrips, such as polyimide tape strips 80, on the border regions 36 and38 of the flexible tape 20 which extend into the cut-out region 72. FIG.7 shows a fragmentary view of the carrier frame 52 including thepolyimide tape strips 80 attached to the borders 36 and 38 of theflexible tape 20 extending into the cut-out region 72. The first ends ofthe tape strips 80 are attached to the flexible tape 20 and the secondends of the adhesive strips 80 are attached to the carrier frame 52adjacent the cut-out region 72.

Referring to FIGS. 8A and 8B, after the flexible tape 20 has beenpivotally connected to the carrier frame 52 by the adhesive strips 80,the carrier frame is lifted off of the work holder and the carrier frame52 is inverted so that the top surface 54 of the frame and the firstsurface 22 of the flexible tape 20 (i.e., the surface bearing theattachment surfaces 27 of the connection components 26) face upwards.The second surface 24 of the flexible tape 20 remains in contact withthe top surface 54 of the carrier frame 52.

Referring to FIGS. 9A and 9B, the carrier frame 52 including theflexible tape 20 is then loaded into a storage magazine 82 for storingthe flexible tape 20 until it is needed for further assembly steps. Themagazine 82 has a plurality of slots 84. As shown in FIG. 9B, each slotis defined by lower ledges 85 and upper ledges 87 facing the lowerledges. The lower ledges are provided with recesses 89 about 0.025inches deep. The recesses provide clearance for the flexible strips 86so that the strips 86 are not damaged by the slots 84 when the carrierframe 52 is stored in the magazine 82. In other preferred embodiments,the carrier frame 52 is not rotated after the flexible strips 86 areattached to the flexible tape 20. In these embodiments, the carrierframes 52 are directly loaded into the magazine slots 84 for storage andafter a predetermined number of carrier frames have been stored insidethe magazine 82, the entire magazine is rotated so that the firstsurfaces 22 of the flexible tapes 20 face upward.

In the next stage of the assembly process, the carrier frame is removedfrom the storage magazine 82 and oriented as shown in FIG. 10A so thatthe flexible tape 20 overlies the top surface 54 of the carrier frame52. In this particular orientation, the top surface 22 of the tape 20faces away from the carrier frame 52 and the second surface 24 of thetape 20 is in contact with the carrier frame 52. A supporting plate 91is provided through the slot in the carrier frame to support theflexible tape 20 from flexing during further assembly steps as will bediscussed below.

Referring to FIG. 10B, resilient elements may then be formed on thefirst surface 22 of the flexible tape 20 according to the embodimentsdisclosed in the aforementioned U.S. Pat. No. 5,659,952 patent. Eachresilient element preferably includes a plurality or array of compliantpads 88 which are desirably stencil printed over the attachment regions.When the resilient elements are provided on the flexible tape 20, it iscritical that the flexible tape 20 overlies the top surface 54 of thecarrier frame 52 so that the bottom surface 93 of a stencil 95 used toform the resilient elements may be flush against the first surface 22 ofthe flexible tape 20. As mentioned above, if the flexible tape 20 werein contact with the bottom surface 56 of the carrier frame 52, thethickness of the carrier frame 52 would prevent the bottom surface 93 ofthe stencil 95 from being flush with the first surface 22 of theflexible tape 20 which would adversely affect the alignment and theshape of the resilient elements. The supporting plate 91 prevents theflexible tape 20 from flexing when the compliant pads 88 are stencilprinted thereon. After the compliant pads 88 have been provided on thetop surface 22 of the flexible tape 20, the stencil 95 is removed andthe compliant pads 88 are later cured as disclosed in the U.S. Pat. No.5,659,952 patent. FIG. 10C shows a top view of one connection component26 of the flexible tape 20 after the compliant pads 88 have been formedthereon.

Before curing, the carrier frames, with tapes and resilient elementsthereon, are loaded into storage magazines identical to or substantiallysimilar to those shown in FIG. 9A. The utilization of the storagemagazine facilitates handling of the flexible tapes 20 during the curingprocesses and isolates the tapes from one another when they are storedin the magazine. The entire magazine can be moved into and out of acuring oven without extraordinary care in handling. After curing theresilient elements, the flexible tape 20 may then be transferred to thebottom surface of the carrier frame 52 in order to complete furtherassembly steps, as will be discussed in more detail below.

FIG. 11 shows a perspective view of a pivoting apparatus used inconjunction with the carrier frame 52 described above for passing theflexible tape 20 through the slot 58 in the carrier frame 52. Thepivoting apparatus 142 includes three separate elements: a base 190which pivots upwards and about an axis designated A--A; a vacuumplatform 192 having vacuum holes 144, and a clamp 194 which is initiallyin an open or raised position directly above the vacuum platform 192.Referring to FIGS. 12A and 12B, the vacuum platform 192 is sized to fitin the center of the base 190 so that the base 190 can rotate about oneend of the vacuum platform 192 along axis A--A. Initially, the topsurface of the vacuum platform 192 in the center of the base 190 isapproximately 500-700 microns higher than the top surface 146 of thebase 190. As shown in FIGS. 13A and 13B, the clamp 194 includes contactribs 196 which extend from one surface of the clamp 194 on oppositesides thereof. Referring to FIG. 13C, the clamp 194 is preferably sizedto fit inside the center of the base 190 and the slot in the carrierframe 52 so that the clamp 194 may remain in contact with the flexibletape 20 as the base 190 pivots about one end of the flexible tape 20.

Referring to FIGS. 14A and 14B, the carrier frame 52 is then alignedwith the carrier frame alignment posts 150 on the base 190 andpositioned in contact with the top surface 146 of the base 190 so thatthe bottom surface 56 of the carrier frame 52 engages the top surface146 of the base 190. In this particular orientation, the first surface22 of the flexible tape 20 faces upward and away from the top surface 54of the carrier frame 52. A vacuum is then activated through the vacuumholes 144 in the vacuum platform 192 so that the second surface 24 ofthe flexible tape 20 is adhered to the vacuum platform 192. As shown inFIGS. 15A and 15B, the clamp 194 is lowered until the contact ribs 196thereon engage the flexible tape 20 adjacent the border regions 36 and38 of the flexible tape 20. The contact ribs 196 are preferablypositioned so that the ribs 196 do not engage the connection components26 or the resilient elements formed on the connection components. Theclamp 194 and the vacuum cooperatively secure the flexible tape 20 in astationary position on the pivoting apparatus

Referring to FIG. 16A, in the next stage of the operation, while theflexible tape 20 is held stationary between the clamp 194 and the vacuumplatform 192, the base 190 and the carrier frame 52 are rotated upwardfrom a first position 198A to a second position 198B, by pivoting thebase 190 and the carrier frame 52 about the A--A axis (shown in FIG.11). In one embodiment, the base 190 and the carrier frame 52 arerotated upward between approximately 20-40°. As the carrier frame 52 isrotated upward, the borders 36 and 38 of the flexible tape 20 disengagefrom the top surface 54 of the carrier frame 52 and the flexible tape 20passes through the slot 58. Referring to FIG. 16B, the carrier frame 52and the base 190 are then rotated downward back to the first position198A so that the bottom surface 56 of the carrier frame 52 in contactwith the first surface 22 of the flexible tape 20 and the slot 58overlies the central region of the flexible tape 20 including theconnection components 26 therein.

FIGS. 17A and 17B show the flexible tape 20 after the tape 20 has passedthrough the slot 58 in the carrier frame 52 and after the carrier framehas been off-loaded from the work holder 142. At this stage, the firstsurface 22 of the tape 20 is in contact with the bottom 56 of thecarrier frame 52 and the slot 58 overlies the connection components 26and the compliant pads 88 formed on the connection components.

Referring to FIGS. 18 and 19, the carrier frame 52 is then inverted sothat the bottom surface 56 of the carrier frame 52 and the secondsurface 24 of the flexible tape 20 face upward. Referring to FIG. 19,additional adhesive strips 80' are then placed over the side borders 36and 38 of the flexible tape 20 to prepare the tape for further stages ofthe process during which microelectronic elements, such as semiconductorchips having electrical contacts on a front face thereof, will beassembled with the connection components of the flexible tape.

FIG. 20 shows a fragmentary side view of later stages of the assemblyprocess during which semiconductor chips 102 are assembled to thecompliant pads 88 on the first surface 22 of the flexible tape 20.Before the semiconductor chips 102 are assembled to the flexible tape20, a supporting plate 191 is preferably placed through the slot 58 inthe carrier frame 52 so that the supporting plate 191 engages the secondsurface 24 of the flexible tape 20. After the supporting plate 191 is inplace, the semiconductor chips 102 are assembled with the connectioncomponents 26 by abutting the front contact bearing faces 104 of thechips 102 against the compliant pads 88 of each connection component 26,whereby the supporting plate 191 prevents undesirable movement andflexing of the flexible tape 20 during the die attach operation.

After die attach, the carrier frame is inverted once again so that thesecond surface of the flexible tape is accessible for bonding theflexible leads to the contacts on the chip. A curable liquid encapsulantmay then be introduced between the chips and the connection componentsas described in the U.S. Pat. No. 5,659,952 patent and the encapsulantcured, using energy such as heat or ultraviolet light, to provide acompliant interface for the chip packages. After the encapsulant iscured, the assemblies may be severed from one another to provideindividual microelectronic assemblies. In certain preferred embodiments,one or more coverlays may be provided over the exterior surfaces of theassemblies while the curable liquid encapsulant is introduced to preventthe encapsulant from contacting the exterior surfaces thereof asdisclosed in U.S. patent application Ser. No. 08/726,697, the disclosureof which is incorporated by reference herein.

Typically, before the flexible tape is severed to provide individualassemblies, solder balls are attached to the terminals at the secondsurface of the flexible tape. Attachment of the solder balls enables theterminals to be electrically connected to an external circuit element,such as a printed circuit board (PCB). One preferred method forattaching solder balls includes providing a flux material over theterminals, such as by using a stencil having an array of holes extendingtherethrough. After the array of holes are aligned over the terminals,the flux is forced through the holes to form flux pads over each of theterminals. Solder balls are then placed on the array of flux pads usinga second stencil fixture having a plurality of holes. A sweeper platemay be used to sweep the solder balls over the matrix of holes.

After the solder balls have been disposed on the flux pads the solderballs are reflowed to form a permanent bond with the terminals.

There are a number of methods which can be used to reflow solder balls.In one preferred embodiment, the flexible tape including the solderballs is placed on a belt which passes the flexible tape through afurnace. In the furnace, the solder balls are heated above a reflowtemperature or melt point and maintained at that temperature forapproximately 30-45 seconds. The solder balls are then cooled down belowthe reflow temperature at which point the solder balls solidify. Theflexible tape and reflowed solder balls may then be processed to removeexcess flux therefrom. The flux removal process, generally referred toas defluxing, can be either a manual procedure or a fully automatedprocedure. In accordance with one preferred manual procedure, theflexible tape bearing the reflowed solder balls is immersed in liquidalcohol for one minute in order to soften the excess flux at theterminal sites and the flexible tape and terminals are then scrubbedwith a brush to remove the excess flux therefrom.

Referring to FIG. 21, in another embodiment, the carrier frame 252 has aslot 258 therein which includes a plurality of teeth 259. The pluralityof teeth 259 extend from opposite sides of the slot 258, toward thecenter of the slot 258. The side borders of the flexible tape (notshown) preferably contact the teeth 259 to maintain the tape on the topor bottom surface of the carrier frame, as may be required during thevarious assembly steps described above.

As will be appreciated, numerous variations and combinations of thefeatures discussed above can be utilized without departing from thepresent invention as defined by the claims. Accordingly, the foregoingdescription of the preferred embodiments should be taken by way ofillustration rather than by way of limitation of the invention.

We claim:
 1. A method of making a microelectronic assembly comprisingthe steps of:(a) providing a flexible tape having first and secondsurfaces and including a plurality of connection components in a centralregion thereof; (b) providing a carrier frame having top and bottomsurfaces and a slot extending therebetween and placing said flexibletape in contact with the top surface of said carrier frame; then (c)performing a first processing operation applying material to said firstsurface on said flexible tape; and then (d) passing said flexible tapethrough said slot so that said flexible tape is in contact with thebottom surface of said carrier frame so that said first surface isaccessible.
 2. A method as claimed in claim 1, wherein the passing stepincludes the steps of:pivotally securing a portion of said flexible tapeto said carrier frame; rotating said carrier frame about the pivotallysecured portion of said flexible tape from a first position toward asecond position while holding said flexible tape substantiallystationary so that said flexible tape disengages from the top surface ofsaid carrier frame and passes through said slot; rotating said carrierframe from said second position back toward said first position so thatthe bottom surface of said carrier frame contacts said flexible tape. 3.A method as claimed in claim 2, wherein said carrier frame comprises oneor more inner edges defining said slot.
 4. A method as claimed in claim3, wherein said flexible tape includes side border regions, the width ofsaid flexible tape being greater than the width of said slot so thatsaid side border regions of said flexible tape extend beyond the widthof said slot when said flexible tape is substantially parallel to saidcarrier frame.
 5. A method as claimed in claim 4, wherein said carrierframe includes a cut-out region contiguous with one end of the slot, thewidth of said cutout region being greater than the width of saidflexible tape.
 6. A method as claimed in claim 5, wherein the pivotallysecuring step includes the step of applying flexible strips including anadhesive to portions of said flexible tape which extend into saidcut-out region.
 7. A method as claimed in claim 6, wherein said borderregions on opposite sides of said flexible tape move toward one anotherduring the passing step.
 8. A method as claimed in claim 1, whereinbefore the passing step the second surface of said flexible tape is incontact with the top surface of said carrier frame.
 9. A method asclaimed in claim 1, wherein after the passing step the first surface ofsaid flexible tape is in contact with the bottom surface of said carrierframe.
 10. A method as claimed in claim 2, wherein after the passingstep said slot overlies and is in substantial alignment with the centralregion of said flexible tape so that said connection components areaccessible through said slot.
 11. A method as claimed in claim 1,wherein said flexible tape has a top surface and a bottom surface, eachsaid connection component including an attachment region at the topsurface of said flexible tape.
 12. A method as claimed in claim 11,wherein the performing a first processing step includes the step ofproviding a resilient element over the attachment region of each saidconnection component.
 13. A method as claimed in claim 12, wherein theproviding said resilient element step includes the step of forming aplurality of compliant pads on each said attachment region.
 14. A methodas claimed in claim 13, wherein the forming a plurality of compliantpads step includes the step of screen printing said compliant pads. 15.A method as claimed in claim 14, further comprising the step of at leastpartially curing said compliant pads.
 16. A method as claimed in claim12, wherein said slot overlies said connection components during theproviding a resilient element step.
 17. A method as claimed in claim 12,wherein the providing said resilient element step includes the step ofmaintaining said flexible tape in a substantially stationary position.18. A method as claimed in claim 1, further comprising the step ofperforming a second processing operation of assembling at least onemicroelectronic element with said flexible tape after the passing step.19. A method as claimed in claim 18, wherein the second processing stepincludes the step of assembling a microelectronic element to each saidconnection component.
 20. A method as claimed in claim 19, wherein eachsaid microelectronic element includes a semiconductor chip havingelectrical contacts.
 21. A method as claimed in claim 19, wherein theassembling step includes the step of maintaining said flexible tape in asubstantially stationary position.
 22. A method as claimed in claim 17,wherein the maintaining step includes the step of placing a supportplate in contact with the second surface of said flexible tape.
 23. Amethod as claimed in claim 19, wherein said assembling step includes thestep of electrically interconnecting each said connection component withone of said microelectronic elements.
 24. A method as claimed in claim23, further comprising the step of providing a curable liquidencapsulant between each said microelectronic element and saidconnection component after the electrically connecting step.
 25. Amethod as claimed in claim 24, further comprising the step of curingsaid curable liquid encapsulant after the providing said curable liquidencapsulant step.
 26. A method as claimed in claim 25, wherein each saidconnection component includes electrically conductive parts.
 27. Amethod as claimed in claim 26, wherein said electrically conductiveparts include a plurality of terminals accessible at a surface of saidflexible tape and flexible leads integrally connected thereto.
 28. Amethod as claimed in claim 27, further comprising the step of attachinga plurality of solder balls to said terminals.
 29. A method as claimedin claim 28, said attaching a plurality of solder balls step includingthe steps of:providing a flux material over said plurality of terminals;providing said solder balls over said flux; reflowing said solder ballsto form a permanent bond between said solder balls and said terminals.30. A method as claimed in claim 29, wherein said reflowing stepincludes the step of heating said solder balls.
 31. A method as claimedin claim 29, further comprising the step of removing excess flux fromsaid flexible tape and said terminals after said reflowing step.
 32. Amethod as claimed in claim 25, further comprising the step of severingsaid flexible tape after the curing step to provide individualmicroelectronic assemblies.
 33. A method as claimed in claim 1, whereinsaid flexible tape includes a dielectric material.
 34. A method asclaimed in claim 1, wherein each said connection component includeselectrically conductive parts.
 35. A method as claimed in claim 33,wherein said electrically conductive parts includes a plurality ofterminals accessible at a surface of said flexible tape and flexibleleads integrally connected thereto.